Methods and apparatus for adaptive motion vector candidate  ordering for video encoding and decoding

ABSTRACT

Methods and apparatus are provided for adaptive motion vector candidate ordering for video encoding and decoding. An apparatus includes a video encoder for encoding a block in a picture by selecting an order of motion vector predictor candidates for the block responsive to a characteristic available at both the video encoder and a corresponding decoder. The characteristic excludes a mode in which the block is partitioned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 61/346,539, filed May 20, 2010, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present principles relate generally to video encoding and decodingand, more particularly, to methods and apparatus for adaptive motionvector candidate ordering for video encoding and decoding.

BACKGROUND

Motion estimation and compensation are widely used in video compressionto exploit the temporal redundancy included in a video sequence. Motioninformation is typically included in motion vectors. A motion vector isthe displacement between the current block and its temporalcorrespondence in the reference frame(s). Such motion information istransmitted, conveyed, and/or otherwise delivered to the decoder asoverhead. To reduce the overhead bits used for motion information,various predictive coding approaches are used to encode the motionvector of each block by exploiting the correlations among neighboringmotion vectors.

In the current state of the art video coding standard, namely theInternational Organization for Standardization/InternationalElectrotechnical Commission (ISO/IEC) Moving Picture Experts Group-4(MPEG-4) Part 10 Advanced Video Coding (AVC) Standard/InternationalTelecommunication Union, Telecommunication Sector (ITU-T) H.264Recommendation (hereinafter the “MPEG-4 AVC Standard”), a motion vectoris predicted by the median of its spatial causal neighboring motionvectors.

In a first prior art approach, the motion vector predictor selectionprocedure is incorporated into the rate-distortion optimization of acoding block, which is called motion vector competition (MVComp). InMVComp, a coding block has a set of motion vector predictor candidates.This candidate set is composed of motion vectors of spatially ortemporally neighboring blocks. The best motion vector predictor will beselected from the candidate set based on the rate-distortionoptimization. The index of the motion vector predictor in the set willbe explicitly transmitted to the decoder if the set has more than onecandidate. However, transmitting this index may disadvantageouslyconsume a lot of bits.

SUMMARY

These and other drawbacks and disadvantages of the prior art areaddressed by the present principles, which are directed to methods andapparatus for adaptive motion vector candidate ordering for videoencoding and decoding.

According to an aspect of the present principles, there is provided anapparatus. The apparatus includes a video encoder for encoding a blockin a picture by selecting an order of motion vector predictor candidatesfor the block responsive to a characteristic available at both the videoencoder and a corresponding decoder. The characteristic excludes a modein which the block is partitioned.

According to another aspect of the present principles, there is provideda method in a video encoder. The method includes encoding a block in apicture by selecting an order of motion vector predictor candidates forthe block responsive to a characteristic available at both the videoencoder and a corresponding decoder. The characteristic excludes a modein which the block is partitioned.

According to still another aspect of the present principles, there isprovided an apparatus. The apparatus includes a video decoder fordecoding a block in a picture by selecting an order of motion vectorpredictor candidates for the block responsive to a characteristicavailable at both the video decoder and a corresponding encoder. Thecharacteristic excludes a mode in which the block is partitioned.

According to a further aspect of the present principles, there isprovided a method in a video decoder. The method includes decoding ablock in a picture by selecting an order of motion vector predictorcandidates for the block responsive to a characteristic available atboth the video decoder and a corresponding encoder. The characteristicexcludes a mode in which the block is partitioned.

These and other aspects, features and advantages of the presentprinciples will become apparent from the following detailed descriptionof exemplary embodiments, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present principles may be better understood in accordance with thefollowing exemplary figures, in which:

FIG. 1 is a block diagram showing an exemplary video encoder to whichthe present principles may be applied, in accordance with an embodimentof the present principles;

FIG. 2 is a block diagram showing an exemplary video decoder to whichthe present principles may be applied, in accordance with an embodimentof the present principles;

FIG. 3 is a flow diagram showing an exemplary method for adaptive motionvector candidate ordering at a video encoder, in accordance with anembodiment of the present principles;

FIG. 4 is a flow diagram showing an exemplary method for adaptive motionvector candidate ordering at a video decoder, in accordance with anembodiment of the present principles;

FIG. 5 is a flow diagram showing an exemplary method for adaptive motionvector candidate ordering at a video encoder, in accordance with anembodiment of the present principles;

FIG. 6 is a flow diagram showing an exemplary method for adaptive motionvector candidate ordering at a video decoder, in accordance with anembodiment of the present principles;

FIG. 7 is a flow diagram showing an exemplary method for adaptive motionvector candidate ordering at a video encoder, in accordance with anembodiment of the present principles;

FIG. 8 is a flow diagram showing an exemplary method for adaptive motionvector candidate ordering at a video decoder, in accordance with anembodiment of the present principles;

FIG. 9 is a flow diagram showing an exemplary method for adaptive motionvector candidate ordering at a video encoder, in accordance with anembodiment of the present principles;

FIG. 10 is a flow diagram showing an exemplary method for adaptivemotion vector candidate ordering at a video decoder, in accordance withan embodiment of the present principles;

FIG. 11 is a flow diagram showing an exemplary method for adaptivemotion vector candidate ordering at a video encoder, in accordance withan embodiment of the present principles;

FIG. 12 is a flow diagram showing an exemplary method for adaptivemotion vector candidate ordering at a video decoder, in accordance withan embodiment of the present principles;

FIG. 13 is a flow diagram showing an exemplary method for adaptivemotion vector candidate ordering at a video encoder, in accordance withan embodiment of the present principles; and

FIG. 14 is a flow diagram showing an exemplary method for adaptivemotion vector candidate ordering at a video decoder, in accordance withan embodiment of the present principles.

DETAILED DESCRIPTION

The present principles are directed to methods and apparatus foradaptive motion vector candidate ordering for video encoding anddecoding.

The present description illustrates the present principles. It will thusbe appreciated that those skilled in the art will be able to devisevarious arrangements that, although not explicitly described or shownherein, embody the present principles and are included within its spiritand scope.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the presentprinciples and the concepts contributed by the inventor(s) to furtheringthe art, and are to be construed as being without limitation to suchspecifically recited examples and conditions.

Moreover, all statements herein reciting principles, aspects, andembodiments of the present principles, as well as specific examplesthereof, are intended to encompass both structural and functionalequivalents thereof. Additionally, it is intended that such equivalentsinclude both currently known equivalents as well as equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat the block diagrams presented herein represent conceptual views ofillustrative circuitry embodying the present principles. Similarly, itwill be appreciated that any flow charts, flow diagrams, statetransition diagrams, pseudocode, and the like represent variousprocesses which may be substantially represented in computer readablemedia and so executed by a computer or processor, whether or not suchcomputer or processor is explicitly shown.

The functions of the various elements shown in the figures may beprovided through the use of dedicated hardware as well as hardwarecapable of executing software in association with appropriate software.When provided by a processor, the functions may be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which may be shared. Moreover, explicituse of the term “processor” or “controller” should not be construed torefer exclusively to hardware capable of executing software, and mayimplicitly include, without limitation, digital signal processor (“DSP”)hardware, read-only memory (“ROM”) for storing software, random accessmemory (“RAM”), and non-volatile storage.

Other hardware, conventional and/or custom, may also be included.Similarly, any switches shown in the figures are conceptual only. Theirfunction may be carried out through the operation of program logic,through dedicated logic, through the interaction of program control anddedicated logic, or even manually, the particular technique beingselectable by the implementer as more specifically understood from thecontext.

In the claims hereof, any element expressed as a means for performing aspecified function is intended to encompass any way of performing thatfunction including, for example, a) a combination of circuit elementsthat performs that function or b) software in any form, including,therefore, firmware, microcode or the like, combined with appropriatecircuitry for executing that software to perform the function. Thepresent principles as defined by such claims reside in the fact that thefunctionalities provided by the various recited means are combined andbrought together in the manner which the claims call for. It is thusregarded that any means that can provide those functionalities areequivalent to those shown herein.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of” for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Also, as used herein, the words “picture” and “image” are usedinterchangeably and refer to a still image or a picture from a videosequence. As is known, a picture may be a frame or a field.

Additionally, as used herein, the phrase “motion vector competition”refers to the adaptive selection of the order of motion vectorcandidates to be used as predictors. Such motion vector competition canbe performed at the encoder side and/or the decoder side. According tothe present principles, it is to be appreciated that the order of themotion vector candidates is adaptable responsive to some commoncharacteristics available at both the encoder and decoder. Exemplarycharacteristics will be disclosed and described later herein.

Moreover, as used herein, the phrase “consistency of the motion vectors”refers to the similarity between the motion vectors. Such similarity canbe judged, for example, responsive to one or more criterion as specifiedherein as well as readily contemplated by one of skill in this andrelated arts, given the teachings of the present principles providedherein.

Further, as used herein, the phrase “block prediction type” refers to aprediction type used to classify one or more blocks under considerationfor the purposes of the present principles. Also, as used herein, thephrase “block partition type” refers to a partition type used toclassify one or more blocks under consideration for the purposes of thepresent principles. Additionally, as used herein, the phrase “blocklocation” refers to a location of one or more blocks under considerationfor the purposes of the present principles. For example, the blocks maypertain to, e.g., one or more slices, one or more pictures, and soforth. Such blocks may be in the same slice or picture as the currentblock being encoded or decoded, or may be in neighboring slices orpictures.

For purposes of illustration and description, examples are describedherein in the context of improvements over the MPEG-4 AVC Standard,using the MPEG-4 AVC Standard as the baseline for our description andexplaining the improvements and extensions beyond the MPEG-4 AVCStandard. However, it is to be appreciated that the present principlesare not limited solely to the MPEG-4 AVC Standard and/or extensionsthereof. Given the teachings of the present principles provided herein,one of ordinary skill in this and related arts would readily understandthat the present principles are equally applicable and would provide atleast similar benefits when applied to extensions of other standards, orwhen applied and/or incorporated within standards not yet developed.That is, it would be readily apparent to those skilled in the art thatother standards may be used as a starting point to describe the presentprinciples and their new and novel elements as changes and advancesbeyond that standard or any other. It is to be further appreciated thatthe present principles also apply to video encoders and video decodersthat do not conform to standards, but rather confirm to proprietarydefinitions.

Turning to FIG. 1, an exemplary video encoder to which the presentprinciples may be applied is indicated generally by the referencenumeral 100. The video encoder 100 includes a frame ordering buffer 110having an output in signal communication with a non-inverting input of acombiner 185. An output of the combiner 185 is connected in signalcommunication with a first input of a transformer and quantizer 125. Anoutput of the transformer and quantizer 125 is connected in signalcommunication with a first input of an entropy coder 145 and a firstinput of an inverse transformer and inverse quantizer 150. An output ofthe entropy coder 145 is connected in signal communication with a firstnon-inverting input of a combiner 190. An output of the combiner 190 isconnected in signal communication with a first input of an output buffer135.

A first output of an encoder controller 105 is connected in signalcommunication with a second input of the frame ordering buffer 110, asecond input of the inverse transformer and inverse quantizer 150, aninput of a picture-type decision module 115, a first input of amacroblock-type (MB-type) decision module 120, a second input of anintra prediction module 160, a second input of a deblocking filter 165,a first input of a motion compensator 170, a first input of a motionestimator 175, and a second input of a reference picture buffer 180.

A second output of the encoder controller 105 is connected in signalcommunication with a first input of a Supplemental EnhancementInformation (SEI) inserter 130, a second input of the transformer andquantizer 125, a second input of the entropy coder 145, a second inputof the output buffer 135, and an input of the Sequence Parameter Set(SPS) and Picture Parameter Set (PPS) inserter 140.

An output of the SEI inserter 130 is connected in signal communicationwith a second non-inverting input of the combiner 190.

A first output of the picture-type decision module 115 is connected insignal communication with a third input of the frame ordering buffer110. A second output of the picture-type decision module 115 isconnected in signal communication with a second input of amacroblock-type decision module 120.

An output of the Sequence Parameter Set (SPS) and Picture Parameter Set(PPS) inserter 140 is connected in signal communication with a thirdnon-inverting input of the combiner 190.

An output of the inverse quantizer and inverse transformer 150 isconnected in signal communication with a first non-inverting input of acombiner 119. An output of the combiner 119 is connected in signalcommunication with a first input of the intra prediction module 160 anda first input of the deblocking filter 165. An output of the deblockingfilter 165 is connected in signal communication with a first input of areference picture buffer 180. An output of the reference picture buffer180 is connected in signal communication with a second input of themotion estimator 175 and a third input of the motion compensator 170. Afirst output of the motion estimator 175 is connected in signalcommunication with a second input of the motion compensator 170. Asecond output of the motion estimator 175 is connected in signalcommunication with a third input of the entropy coder 145.

An output of the motion compensator 170 is connected in signalcommunication with a first input of a switch 197. An output of the intraprediction module 160 is connected in signal communication with a secondinput of the switch 197. An output of the macroblock-type decisionmodule 120 is connected in signal communication with a third input ofthe switch 197. The third input of the switch 197 determines whether ornot the “data” input of the switch (as compared to the control input,i.e., the third input) is to be provided by the motion compensator 170or the intra prediction module 160. The output of the switch 197 isconnected in signal communication with a second non-inverting input ofthe combiner 119 and an inverting input of the combiner 185.

A first input of the frame ordering buffer 110 and an input of theencoder controller 105 are available as inputs of the encoder 100, forreceiving an input picture. Moreover, a second input of the SupplementalEnhancement Information (SEI) inserter 130 is available as an input ofthe encoder 100, for receiving metadata. An output of the output buffer135 is available as an output of the encoder 100, for outputting abitstream.

Turning to FIG. 2, an exemplary video decoder to which the presentprinciples may be applied is indicated generally by the referencenumeral 200. The video decoder 200 includes an input buffer 210 havingan output connected in signal communication with a first input of anentropy decoder 245. A first output of the entropy decoder 245 isconnected in signal communication with a first input of an inversetransformer and inverse quantizer 250. An output of the inversetransformer and inverse quantizer 250 is connected in signalcommunication with a second non-inverting input of a combiner 225. Anoutput of the combiner 225 is connected in signal communication with asecond input of a deblocking filter 265 and a first input of an intraprediction module 260. A second output of the deblocking filter 265 isconnected in signal communication with a first input of a referencepicture buffer 280. An output of the reference picture buffer 280 isconnected in signal communication with a second input of a motioncompensator 270.

A second output of the entropy decoder 245 is connected in signalcommunication with a third input of the motion compensator 270, a firstinput of the deblocking filter 265, and a third input of the intrapredictor 260. A third output of the entropy decoder 245 is connected insignal communication with an input of a decoder controller 205. A firstoutput of the decoder controller 205 is connected in signalcommunication with a second input of the entropy decoder 245. A secondoutput of the decoder controller 205 is connected in signalcommunication with a second input of the inverse transformer and inversequantizer 250. A third output of the decoder controller 205 is connectedin signal communication with a third input of the deblocking filter 265.A fourth output of the decoder controller 205 is connected in signalcommunication with a second input of the intra prediction module 260, afirst input of the motion compensator 270, and a second input of thereference picture buffer 280.

An output of the motion compensator 270 is connected in signalcommunication with a first input of a switch 297. An output of the intraprediction module 260 is connected in signal communication with a secondinput of the switch 297. An output of the switch 297 is connected insignal communication with a first non-inverting input of the combiner225.

An input of the input buffer 210 is available as an input of the decoder200, for receiving an input bitstream. A first output of the deblockingfilter 265 is available as an output of the decoder 200, for outputtingan output picture.

As noted above, the present principles are directed to methods andapparatus for adaptive motion vector candidate ordering for videoencoding and decoding. In a second prior art approach, the order ofmotion vector predictor candidates is adjusted based on the currentprediction mode to place the most probable motion predictor in the firstposition. We have noticed that the method described in the second priorart approach utilizes only very limited information, i.e., theprediction mode of the current block. The prediction mode refers to themanner in which a block is partitioned. We have recognized thelimitations inherent in the second prior art approach, namely, limitingthe ordering based on the manner in which a block is partitioned.Advantageously and in accordance with the present principles, we havedeveloped methods and apparatus for using more readily availableinformation to determine the order of motion vector candidates such thatthe motion vector predictor that is more frequently selected tends tohave a smaller index and, thus, the overhead bits for the motion vectorpredictor index can be reduced.

Thus, in accordance with the present principles, we provide an adaptivemotion vector competition scheme (that is, a motion vector orderingscheme), where the order of motion vector predictor candidates isadaptively determined based on some common information available at boththe encoder and the decoder. In one or more embodiments, the commoninformation includes, but is not limited to, one or more of thefollowing: the selection frequency of the motion vector predictorcandidates in the already encoded blocks; the block type of the currentblock; the consistency of the motion vector predictor candidates; thefidelity of the motion vector predictor candidates; the reference indexof the motion vector predictor candidates; and the predictor index ofthe first motion vector component.

In an embodiment utilizing adaptive ordering, smaller indices areassigned to the motion vector predictors that tend to be more frequentlyselected and, thus, the overhead bits for the motion vector predictorindex can be reduced. That is, we provide methods and apparatus forperforming adaptive motion vector competition to reduce the overheadbits of conveying the index of the selected motion vector predictor andimprove the coding efficiency.

For purposes of clarity and definition, we use the term motion vectorcompetition to mean that the encoder and decoder adaptively select theorder of motion vector candidates to be used as predictors. This meansthat the order is adaptable depending upon some common characteristic(s)available at both the encoder and decoder. Some exemplarycharacteristics are described herein. The candidates in the motionvector predictor set are motion vectors of the spatially neighboringblocks (e.g., the left block, the right block, the top block, the righttop block, and so forth), motion vectors of the temporally neighboringblocks (e.g., the co-located block(s) in the reference frame(s)), andthe function (e.g., the median value or some other value) of some motionvector candidates. In addition, candidates may be selected and orderedthat are not in spatially or temporally neighboring blocks, but ratherselected and ordered by some other defining characteristic. In anembodiment, the order of these candidates in the set is determinedaccording to some common information available at both the encoder andthe decoder such that the motion vector predictor that is morefrequently selected tends to have a smaller index. Therefore, theoverhead bits for the motion vector predictor index can be reduced. Itshould be noted that the adaptive ordering of the motion vectorpredictor is equivalent to the adaptive index of the motion vectorpredictor and, thereafter, we will use these two terms interchangeably.

Embodiment 1

In Embodiment 1, we use the selection frequency of the motion vectorcandidates in the already encoded blocks to determine the order of themotion vector candidates. One example is as follows: before encoding ablock in the current frame, the encoder collects the frequency of amotion vector predictor candidate being selected in a number ofpreviously encoded blocks, slices, or frames. Let MV_(i) be a motionvector candidate, and f(MV_(i)) be the frequency at which that motionvector candidate is selected. For encoding the current block, we arrangethe motion vector candidates in a descending order of the selectionfrequency f(MV_(i)), i.e., a motion vector candidate with a higherfrequency has a smaller index. The same procedure is applied at thedecoder with information available at the decoder and therefore the samedetermination is made at the decoder implicitly, thereby reducing therequired bit overhead.

Turning to FIG. 3, an exemplary method for adaptive motion vectorcandidate ordering at a video encoder is indicated generally by thereference numeral 300. The method 300 corresponds to Embodiment 1. Themethod 300 includes a start block 305 that passes control to a looplimit block 310. The loop limit block 310 begins a loop using a variablei having a range from 0 to the num_blocks_minus1, and passes control toa function block 315. The function block 315 sets the order of themotion vector predictor candidates based on the selection frequency inalready encoded blocks from a number of previous blocks or a number ofprevious slices or a number of previous frames, and passes control to afunction block 320. The function block 320 performs motion estimation tofind the motion vector of the current block, selects the motion vectorpredictor from the candidates, and passes control to a function block325. The function block 325 encodes the block, and passes control to afunction block 330. The function block 330 writes the index of theselected motion vector predictor and other information into a bitstream,and passes control to a loop limit block 335. The loop limit block 335ends the loop, and passes control to an end block 399.

Turning to FIG. 4, an exemplary method for adaptive motion vectorcandidate ordering at a video decoder is indicated generally by thereference numeral 400. The method 400 corresponds to Embodiment 1. Themethod 400 includes a start block 405 that passes control to a looplimit block 410. The loop limit block 410 begins a loop using a variablei having a range from 0 to the num_blocks_minus1, and passes control toa function block 415. The function block 415 sets the order of themotion vector predictor candidates based on the selection frequency inalready encoded blocks from a number of previous blocks or a number ofprevious slices or a number of previous frames, and passes control to afunction block 420. The function block 420 decodes the index of themotion vector predictor and other information from the bitstream, andpasses control to a function block 425. The function block 425 obtainsthe motion vector predictor according to the index, reconstructs themotion vector, reconstructs the block, and passes control to a looplimit block 430. The loop limit block 430 ends the loop, and passescontrol to an end block 499.

Embodiment 2

In Embodiment 2, we first classify blocks into different categories. Theclassification criterion can be the prediction type of a block (e.g.,predictive (P) or bi-predictive (B) type prediction), the partition typeof a block (e.g., partition size), the location of a block relative toavailable predictors (e.g., the nearest available predictor block isoften the best candidate, but is not always so), and so forth. Wecollect the selection frequency of the motion vector candidates for thealready encoded blocks in each category. Let MV_(i) be a motion vectorcandidate, and f(MV_(i), C_(j)) be the selection frequency of thatmotion vector candidate for category C_(j) blocks in a number of thepreviously encoded blocks, slices or frames. Presuming that the currentblock belonging to category C_(j), we adjust the motion vector candidateindex according to f(MV_(i), C_(j)). Specifically, a motion vectorcandidate MV_(k) with a higher frequency f(MV_(k), C_(j)) has a smallerindex. The same procedure is applied at the decoder with informationavailable at the decoder and, therefore, the same determination is madeat the decoder implicitly, thereby reducing the required bit overhead.

Turning to FIG. 5, an exemplary method for adaptive motion vectorcandidate ordering at a video encoder is indicated generally by thereference numeral 500. The method 500 corresponds to Embodiment 2. Themethod 500 includes a start block 505 that passes control to a looplimit block 510. The loop limit block 510 begins a loop using a variablei having a range from 0 to the num_blocks_minus1, and passes control toa function block 515. The function block 515 obtains the category of thecurrent block based on block prediction type, block partition type,block location, and so forth, and passes control to a function block520. The function block 520 sets the order of the motion vectorpredictor candidates based on the selection frequency in already encodedblocks belonging to the same category, which are from a number ofprevious blocks or a number of previous slices or a number of previousframes, and passes control to a function block 525. The function block525 performs motion estimation to find the motion vector of the currentblock, selects the motion vector predictor from the candidates, andpasses control to a function block 530. The function block 530 encodesthe block, and passes control to a function block 535. The functionblock 535 writes the index of the selected motion vector predictor andother information into a bitstream, and passes control to a loop limitblock 540. The loop limit block 540 ends the loop, and passes control toan end block 599.

Turning to FIG. 6, an exemplary method for adaptive motion vectorcandidate ordering at a video decoder is indicated generally by thereference numeral 600. The method 600 corresponds to Embodiment 2. Themethod 600 includes a start block 605 that passes control to a looplimit block 610. The loop limit block 610 begins a loop using a variablei having a range from 0 to the num_blocks_minus1, and passes control toa function block 615. The function block 615 decodes the syntax of thecurrent block from the bitstream, and passes control to a function block620. The function block 620 obtains the category of the current blockbased on block prediction type, block partition type, block location,and so forth, and passes control to a function block 625. The functionblock 625 sets the order of the motion vector predictor candidates basedon the selection frequency in already decoded blocks from a number ofprevious blocks or a number of previous slices or a number of previousframes, and passes control to a function block 630. The function block630 obtains the motion vector predictor according to the received motionvector predictor index, and passes control to a function block 635. Thefunction block 635 reconstructs the motion vector, reconstructs theblock, and passes control to a loop limit block 640. The loop limitblock 640 ends the loop, and passes control to an end block 699.

Embodiment 3

In Embodiment 3, we first classify the motion vector candidates of thecurrent block into different categories based on the consistency of themotion vectors. As noted above, the consistency of the motion vectorsrefers to the similarity between the motion vectors. An example methodof grouping motion vectors based on their consistency (similarity) is asfollows: Let C_(i) be a group, for any two motion vectors, e.g.,MV_(a)=(MVX_(a), MVY_(a)) and MV_(b)=(MVX_(b), MVY_(b)) belonging twothis group, their difference is smaller than a threshold T, i.e.,|MVX_(a)−MVX_(b)|+|MVY_(a)−MVY_(b)|<T. Suppose we have N categories, C₀,C₁, . . . C_(N-1). We assign the index of motion vector predictor in aninterleaving manner. An example is as follows: index 0 to index N−1 aregiven to the first elements in C₀ to C_(N-1) respectively; index N toindex 2N−1 are given to the second elements in C₀ to C_(N-1)respectively; and so forth. The same procedure is applied at the decoderwith information available at the decoder and therefore the samedetermination is made at the decoder implicitly, thereby reducing therequired bit overhead.

Turning to FIG. 7, an exemplary method for adaptive motion vectorcandidate ordering at a video encoder is indicated generally by thereference numeral 700. The method 700 corresponds to Embodiment 3. Themethod 700 includes a start block 705 that passes control to a looplimit block 710. The loop limit block 710 begins a loop using a variablei having a range from 0 to the num_blocks_minus1, and passes control toa function block 715. The function block 715 sets the order of themotion vector predictor candidates based on their consistency, andpasses control to a function block 720. The function block 720 performsmotion estimation to find the motion vector of the current block,selects the motion vector predictor from the candidates, and passescontrol to a function block 725. The function block 725 encodes theblock, and passes control to a function block 730. The function block730 writes the index of the selected motion vector predictor and otherinformation into a bitstream, and passes control to a loop limit block735. The loop limit block 735 ends the loop, and passes control to anend block 799.

Turning to FIG. 8, an exemplary method for adaptive motion vectorcandidate ordering at a video decoder is indicated generally by thereference numeral 800. The method 800 corresponds to Embodiment 3. Themethod 800 includes a start block 805 that passes control to a looplimit block 810. The loop limit block 810 begins a loop using a variablei having a range from 0 to the num_blocks_minus1, and passes control toa function block 815. The function block 815 sets the order of themotion vector predictor candidates based on their consistency, andpasses control to a function block 820. The function block 820 decodesthe index of the motion vector predictor and other information from thebitstream, and passes control to a function block 825. The functionblock 825 obtains the motion vector predictor according to the index,reconstructs the motion vector, reconstructs the block, and passescontrol to a loop limit block 830. The loop limit block 830 ends theloop, and passes control to an end block 899.

Embodiment 4

In Embodiment 4, we calculate a fidelity value for each motion vectorcandidate of the current block. The fidelity value reflects the accuracyof the motion vector. One example of calculating the fidelity value isas follows: Let candidate MV_(i) be the MV from block Blk_(i). Thefidelity value of MV_(i), F(MV_(i)) is the function of the reconstructedresidue E_(i) of block Blk_(i), calculated as follows:

F(MV_(i))=f(E _(i)).

The function should be a decreasing function of residue E_(i), whichmeans a larger residue results in a lower fidelity. We arrange themotion vector candidates in descending order of the fidelity value,i.e., a motion vector candidate with a higher fidelity value F(MV_(i))has a smaller index. The same procedure is applied at the decoder withinformation available at the decoder and therefore the samedetermination is made at the decoder implicitly, thereby reducing therequired bit overhead.

Turning to FIG. 9, an exemplary method for adaptive motion vectorcandidate ordering at a video encoder is indicated generally by thereference numeral 900. The method 900 corresponds to Embodiment 4. Themethod 900 includes a start block 905 that passes control to a looplimit block 910. The loop limit block 910 begins a loop using a variablei having a range from 0 to the num_blocks_minus1, and passes control toa function block 915. The function block 915 sets the order of themotion vector predictor candidates based on their fidelity, and passescontrol to a function block 920. The function block 920 performs motionestimation to find the motion vector of the current block, selects themotion vector predictor from the candidates, and passes control to afunction block 925. The function block 925 encodes the block, and passescontrol to a function block 930. The function block 930 writes the indexof the selected motion vector predictor and other information into abitstream, and passes control to a loop limit block 935. The loop limitblock 935 ends the loop, and passes control to an end block 999.

Turning to FIG. 10, an exemplary method for adaptive motion vectorcandidate ordering at a video decoder is indicated generally by thereference numeral 1000. The method 1000 corresponds to Embodiment 4. Themethod 1000 includes a start block 1005 that passes control to a looplimit block 1010. The loop limit block 1010 begins a loop using avariable i having a range from 0 to the num_blocks_minus1, and passescontrol to a function block 1015. The function block 1015 sets the orderof the motion vector predictor candidates based on their fidelity, andpasses control to a function block 1020. The function block 1020 decodesthe index of the motion vector predictor and other information from thebitstream, and passes control to a function block 1025. The functionblock 1025 obtains the motion vector predictor according to the index,reconstructs the motion vector, reconstructs the block, and passescontrol to a loop limit block 1030. The loop limit block 1030 ends theloop, and passes control to an end block 1099.

Embodiment 5

Motion vector candidates are motion vectors of the spatially or temporalneighboring blocks, and each of them is associated with a referenceframe index. In Embodiment 5, we arrange the order of the motion vectorcandidates based on the reference frame index. One example is asfollows: suppose r_(c) is the reference frame index of the currentblock. For a motion vector predictor candidate MV_(i) with referenceframe index r_(i), we calculate its reference frame difference withrespect to the current block, d_(i)=abs(r_(i)−r_(c)), and arrange themotion vector candidate in a descending order of the reference frameindex difference d_(i). The same procedure is applied at the decoderwith information available at the decoder and therefore the samedetermination is made at the decoder implicitly, thereby reducing therequired bit overhead.

Turning to FIG. 11, an exemplary method for adaptive motion vectorcandidate ordering at a video encoder is indicated generally by thereference numeral 1100. The method 1100 corresponds to Embodiment 5. Themethod 1100 includes a start block 1105 that passes control to a looplimit block 1110. The loop limit block 1110 begins a loop using avariable i having a range from 0 to the num_blocks_minus1, and passescontrol to a function block 1115. The function block 1115 sets the orderof the motion vector predictor candidates based on the reference frameindex, and passes control to a function block 1120. The function block1120 performs motion estimation to find the motion vector of the currentblock, selects the motion vector predictor from the candidates, andpasses control to a function block 1125. The function block 1125 encodesthe block, and passes control to a function block 1130. The functionblock 1130 writes the index of the selected motion vector predictor andother information into a bitstream, and passes control to a loop limitblock 1135. The loop limit block 1135 ends the loop, and passes controlto an end block 1199.

Turning to FIG. 12, an exemplary method for adaptive motion vectorcandidate ordering at a video decoder is indicated generally by thereference numeral 1200. The method 1200 corresponds to Embodiment 5. Themethod 1200 includes a start block 1205 that passes control to a looplimit block 1210. The loop limit block 1210 begins a loop using avariable i having a range from 0 to the num_blocks_minus1, and passescontrol to a function block 1215. The function block 1215 decodes thesyntax of the current block from the bitstream, and passes control to afunction block 1220. The function block 1220 sets the order of themotion vector predictor candidates based on the reference frame index,and passes control to a function block 1225. The function block 1225obtains the motion vector predictor according to the received index,reconstructs the motion vector, reconstructs the block, and passescontrol to a loop limit block 1230. The loop limit block 1230 ends theloop, and passes control to an end block 1299.

Embodiment 6

Motion vector candidate selection (MVComp) can be applied to eachcomponent of a motion vector. Using the motion vector horizontalcomponent mv_x as an example, such component can have multiple predictorcandidates, which are the horizontal components of the motion vector ofthe spatially and temporally neighboring blocks, and an index idx_x istransmitted to signal which predictor is used. Similarly, the verticalcomponent mv_y also can have multiple predictor candidates, and an indexidx_y is transmitted. Suppose idx_x is transmitted before transmittingmv_y. The order of predictor candidates for mv_y can be adjusted basedon the value of idx_x. One example is as follows: suppose candidatemv_x, belonging to mv_(i) is selected as the predictor of mv_x, and itsindex is idx_x_(i). Let mv_y_(j) belonging to mv_(j) be a candidate ofmv_y. We calculate the difference between mv_(j) and mv_(i). Forexample, an mv_y_(j) with a larger difference will have a larger index.At the decoder side, the decoder obtains mv_x_(i) based on the receivedidx_x_(i). The same procedure is applied at the decoder with informationavailable at the decoder and therefore the same determination is made atthe decoder implicitly, thereby reducing the required bit overhead.

Turning to FIG. 13, an exemplary method for adaptive motion vectorcandidate ordering at a video encoder is indicated generally by thereference numeral 1300. The method 1300 corresponds to Embodiment 6. Themethod 1300 includes a start block 1305 that passes control to a looplimit block 1310. The loop limit block 1310 begins a loop using avariable i having a range from 0 to the num_blocks_minus1, and passescontrol to a function block 1315. The function block 1315 performsmotion estimation to find the motion vector (MV) of the current block,and passes control to a function block 1320. The function block 1320selects the motion vector predictor for the first component, and passescontrol to the function block 1325. The function block 1325 sets theorder of the motion vector predictor candidates of the second componentbased on the predictor of the first component, and passes control to thefunction block 1330. The function block 1330 encodes the block, andpasses control to the function block 1335. The function block 1335writes the predictor index of both motion vector components and otherinformation into a bitstream, and passes control to a loop limit block1340. The loop limit block 1340 ends the loop, and passes control to anend block 1399.

Turning to FIG. 14, an exemplary method for adaptive motion vectorcandidate ordering at a video decoder is indicated generally by thereference numeral 1400. The method 1400 corresponds to Embodiment 6. Themethod 1400 includes a start block 1405 that passes control to a looplimit block 1410. The loop limit block 1410 begins a loop using avariable i having a range from 0 to the num_blocks_minus1, and passescontrol to a function block 1415. The function block 1415 decodes thesyntax of the current block from the bitstream, and passes control to afunction block 1420. The function block 1420, with the receivedpredictor index of the first motion vector component, obtains the motionvector predictor of the first component, and passes control to afunction block 1425. The function block 1425 sets the order of themotion vector predictor candidates for the second motion vectorcomponents based on the motion vector predictor of the first component,and passes control to a function block 1430. The function block 1430,with the received predictor index of the second motion vector component,obtains the motion vector predictor of the second component, and passescontrol to a function block 1435. The function block 1435 reconstructsthe motion vector, reconstructs the block, and passes control to a looplimit block 1440. The loop limit block 1440 ends the loop, and passescontrol to an end block 1499.

Syntax

TABLE 1 shows exemplary slice header syntax, in accordance with anembodiment of the present principles.

TABLE 1 slice_header( ) { Descriptor  ...  adaptive_mvp_ordering_flagu(1)  ...  if (adaptive_mvp_ordering_flag)   {   adaptive_mvp_ordering_mode u(v)  }  ...  }

The semantics of the syntax elements shown in TABLE 1 are as follows:

adaptive_mvp_ordering_flag specifies whether adaptive motion vectorcompetition is used. adaptive_mvp_ordering_flag equal to 1 meansadaptive ordering is used for motion vector competition.adaptive_mvp_ordering_flag equal to 0 means adaptive ordering is notused for motion vector competition

adaptive_mvp_ordering_mode specifies the adaptive ordering method usedfor this slice. adaptive_mvp_ordering_mode=0 indicates that adaptiveordering based on the selection frequency of motion vector candidate inthe already encoded blocks is used (an example method is given inEmbodiment 1). adaptive_mvp_ordering_mode=1 indicates that adaptiveordering based on the selection frequency of motion vector candidate inthe already encoded blocks belonging to the same category as the currentblock is used (an example method is given in Embodiment 2).adaptive_mvp_ordering_mode=2 indicates that adaptive ordering based onthe consistency of motion vector predictor candidates is used (anexample method is given in Embodiment 3). adaptive_mvp_ordering_mode=3indicates that adaptive ordering based on the fidelity of motion vectorpredictor candidates is used (an example method is given in Embodiment4). adaptive_mvp_ordering_mode=4 indicates that adaptive ordering basedon the reference frame index of motion vector predictor candidates isused (an example method is given in Embodiment 5).adaptive_mvp_ordering_mode=5 indicates that each motion vector componenthas its own predictor index, and the predictor candidates ordering ofthe second component is adapted on the received predictor index of thefirst component (an example method is given in Embodiment 6).

A description will now be given of some of the many attendantadvantages/features of the present invention, some of which have beenmentioned above. For example, one advantage/feature is an apparatushaving a video encoder for encoding a block in a picture by selecting anorder of motion vector predictor candidates for the block responsive toa characteristic available at both the video encoder and a correspondingdecoder, wherein the characteristic excludes a mode in which the blockis partitioned.

Another advantage/feature is the apparatus having the video encoder asdescribed above, wherein the characteristic includes a motion vectorcandidate selection frequency in a number of already encoded blocks.

Yet another advantage/feature is the apparatus having the video encoderwherein the characteristic includes a motion vector candidate selectionfrequency in a number of already encoded blocks as described above,wherein a category classification is performed to determine one of aplurality of categories to which the block belongs, and the motionvector candidate selection frequency is determined from the number ofalready encoded blocks that belong to the same one of the plurality ofcategories as the block.

Still another advantage/feature is the apparatus having the videoencoder wherein a category classification is performed to determine oneof a plurality of categories to which the block belongs, and the motionvector candidate selection frequency is determined from the number ofalready encoded blocks that belong to the same one of the plurality ofcategories as the block as described above, wherein a criterion for thecategory classification is a block prediction type.

Moreover, another advantage/feature is the apparatus having the videoencoder wherein a category classification is performed to determine oneof a plurality of categories to which the block belongs, and the motionvector candidate selection frequency is determined from the number ofalready encoded blocks that belong to the same one of the plurality ofcategories as the block as described above, wherein a criterion for thecategory classification is a block partition type.

Further, another advantage/feature is the apparatus having the videoencoder wherein a category classification is performed to determine oneof a plurality of categories to which the block belongs, and the motionvector candidate selection frequency is determined from the number ofalready encoded blocks that belong to the same one of the plurality ofcategories as the block as described above, wherein a criterion for thecategory classification is a block location.

Also, another advantage/feature is the apparatus having the videoencoder as described above, wherein the characteristic includes aconsistency of the motion vector predictor candidates.

Additionally, another advantage/feature is the apparatus having thevideo encoder wherein the characteristic includes a consistency of themotion vector predictor candidates as described above, wherein theconsistency is a function of a difference between the motion vectorpredictor candidates that are available at both the video encoder andthe corresponding decoder.

Moreover, another advantage/feature is the apparatus having the videoencoder as described above, wherein the characteristic includes afidelity of the motion vector predictor candidates.

Further, another advantage/feature is the apparatus having the videoencoder wherein the characteristic includes a fidelity of the motionvector predictor candidates as described above, wherein the fidelity isa function of corresponding reconstructed residue coefficients which areavailable at both the video encoder and the corresponding decoder.

Also, another advantage/feature is the apparatus having the videoencoder as described above, wherein the characteristic includes areference frame index of the motion vector predictor candidates.

Additionally, another advantage/feature is the apparatus having thevideo encoder as described above, wherein the motion vector predictorcandidates include a first motion vector predictor candidate for a firstcomponent of a motion vector and a second motion vector predictorcandidate for a second component of the motion vector, and an order ofthe second motion vector predictor candidate for the second component isadapted responsive to a predictor index of the first component.

These and other features and advantages of the present principles may bereadily ascertained by one of ordinary skill in the pertinent art basedon the teachings herein. It is to be understood that the teachings ofthe present principles may be implemented in various forms of hardware,software, firmware, special purpose processors, or combinations thereof.

Most preferably, the teachings of the present principles are implementedas a combination of hardware and software. Moreover, the software may beimplemented as an application program tangibly embodied on a programstorage unit. The application program may be uploaded to, and executedby, a machine comprising any suitable architecture. Preferably, themachine is implemented on a computer platform having hardware such asone or more central processing units (“CPU”), a random access memory(“RAM”), and input/output (“I/O”) interfaces. The computer platform mayalso include an operating system and microinstruction code. The variousprocesses and functions described herein may be either part of themicroinstruction code or part of the application program, or anycombination thereof, which may be executed by a CPU. In addition,various other peripheral units may be connected to the computer platformsuch as an additional data storage unit and a printing unit.

It is to be further understood that, because some of the constituentsystem components and methods depicted in the accompanying drawings arepreferably implemented in software, the actual connections between thesystem components or the process function blocks may differ dependingupon the manner in which the present principles are programmed. Giventhe teachings herein, one of ordinary skill in the pertinent art will beable to contemplate these and similar implementations or configurationsof the present principles.

Although the illustrative embodiments have been described herein withreference to the accompanying drawings, it is to be understood that thepresent principles is not limited to those precise embodiments, and thatvarious changes and modifications may be effected therein by one ofordinary skill in the pertinent art without departing from the scope orspirit of the present principles. All such changes and modifications areintended to be included within the scope of the present principles asset forth in the appended claims.

1. An apparatus, comprising: a video encoder for encoding a block in apicture by selecting an order of motion vector predictor candidates forthe block responsive to a characteristic available at both the videoencoder and a corresponding decoder, wherein the characteristic excludesa mode in which the block is partitioned.
 2. The apparatus of claim 1,wherein the characteristic comprises a motion vector candidate selectionfrequency in a number of already encoded blocks.
 3. The apparatus ofclaim 2, wherein a category classification is performed to determine oneof a plurality of categories to which the block belongs, and the motionvector candidate selection frequency is determined from the number ofalready encoded blocks that belong to the same one of the plurality ofcategories as the block.
 4. The apparatus of claim 3, wherein acriterion for the category classification is a block prediction type. 5.The apparatus of claim 3, wherein a criterion for the categoryclassification is a block partition type.
 6. The apparatus of claim 3,wherein a criterion for the category classification is a block location.7. The apparatus of claim 1, wherein the characteristic comprises aconsistency of the motion vector predictor candidates.
 8. The apparatusof claim 7, wherein the consistency is a function of a differencebetween the motion vector predictor candidates that are available atboth the video encoder and the corresponding decoder.
 9. The apparatusof claim 1, wherein the characteristic comprises a fidelity of themotion vector predictor candidates.
 10. The apparatus of claim 9,wherein the fidelity is a function of corresponding reconstructedresidue coefficients which are available at both the video encoder andthe corresponding decoder.
 11. The apparatus of claim 1, wherein thecharacteristic comprises a reference frame index of the motion vectorpredictor candidates.
 12. The apparatus of claim 1, wherein the motionvector predictor candidates comprise a first motion vector predictorcandidate for a first component of a motion vector and a second motionvector predictor candidate for a second component of the motion vector,and an order of the second motion vector predictor candidate for thesecond component is adapted responsive to a predictor index of the firstcomponent.
 13. In a video encoder, a method, comprising: encoding ablock in a picture by selecting an order of motion vector predictorcandidates for the block responsive to a characteristic available atboth the video encoder and a corresponding decoder, wherein thecharacteristic excludes a mode in which the block is partitioned. 14.The method of claim 13, wherein the characteristic comprises a motionvector candidate selection frequency in a number of already encodedblocks.
 15. The method of claim 14, wherein a category classification isperformed to determine one of a plurality of categories to which theblock belongs, and the motion vector candidate selection frequency isdetermined from the number of already encoded blocks that belong to thesame one of the plurality of categories as the block.
 16. The method ofclaim 15, wherein a criterion for the category classification is a blockprediction type.
 17. The method of claim 15, wherein a criterion for thecategory classification is a block partition type.
 18. The method ofclaim 15, wherein a criterion for the category classification is a blocklocation.
 19. The method of claim 13, wherein the characteristiccomprises a consistency of the motion vector predictor candidates. 20.The method of claim 19, wherein the consistency is a function of adifference between the motion vector predictor candidates that areavailable at both the video encoder and the corresponding decoder. 21.The method of claim 13, wherein the characteristic comprises a fidelityof the motion vector predictor candidates.
 22. The method of claim 21,wherein the fidelity is a function of corresponding reconstructedresidue coefficients which are available at both the video encoder andthe corresponding decoder.
 23. The method of claim 13, wherein thecharacteristic comprises a reference frame index of the motion vectorpredictor candidates.
 24. The method of claim 13, wherein the motionvector predictor candidates comprise a first motion vector predictorcandidate for a first component of a motion vector and a second motionvector predictor candidate for a second component of the motion vector,and an order of the second motion vector predictor candidate for thesecond component is adapted responsive to a predictor index of the firstcomponent.
 25. An apparatus, comprising: a video decoder for decoding ablock in a picture by selecting an order of motion vector predictorcandidates for the block responsive to a characteristic available atboth the video decoder and a corresponding encoder, wherein thecharacteristic excludes a mode in which the block is partitioned. 26.The apparatus of claim 25, wherein the characteristic comprises a motionvector candidate selection frequency in a number of already encodedblocks.
 27. The apparatus of claim 26, wherein a category classificationis performed to determine one of a plurality of categories to which theblock belongs, and the motion vector candidate selection frequency isdetermined from the number of already encoded blocks that belong to thesame one of the plurality of categories as the block.
 28. The apparatusof claim 27, wherein a criterion for the category classification is ablock prediction type.
 29. The apparatus of claim 27, wherein acriterion for the category classification is a block partition type. 30.The apparatus of claim 27, wherein a criterion for the categoryclassification is a block location.
 31. The apparatus of claim 25,wherein the characteristic comprises a consistency of the motion vectorpredictor candidates.
 32. The apparatus of claim 31, wherein theconsistency is a function of a difference between the motion vectorpredictor candidates that are available at both the video decoder andthe corresponding encoder.
 33. The apparatus of claim 25, wherein thecharacteristic comprises a fidelity of the motion vector predictorcandidates.
 34. The apparatus of claim 33, wherein the fidelity is afunction of corresponding reconstructed residue coefficients which areavailable at both the video decoder and the corresponding encoder. 35.The apparatus of claim 25, wherein the characteristic comprises areference frame index of the motion vector predictor candidates.
 36. Theapparatus of claim 25, wherein the motion vector predictor candidatescomprise a first motion vector predictor candidate for a first componentof a motion vector and a second motion vector predictor candidate for asecond component of the motion vector, and an order of the second motionvector predictor candidate for the second component is adaptedresponsive to a predictor index of the first component.
 37. In a videodecoder, a method, comprising: decoding a block in a picture byselecting an order of motion vector predictor candidates for the blockresponsive to a characteristic available at both the video decoder and acorresponding encoder, wherein the characteristic excludes a mode inwhich the block is partitioned.
 38. The method of claim 37, wherein thecharacteristic comprises a motion vector candidate selection frequencyin a number of already encoded blocks.
 39. The method of claim 38,wherein a category classification is performed to determine one of aplurality of categories to which the block belongs, and the motionvector candidate selection frequency is determined from the number ofalready encoded blocks that belong to the same one of the plurality ofcategories as the block.
 40. The method of claim 39, wherein a criterionfor the category classification is a block prediction type.
 41. Themethod of claim 39, wherein a criterion for the category classificationis a block partition type.
 42. The method of claim 39, wherein acriterion for the category classification is a block location.
 43. Themethod of claim 37, wherein the characteristic comprises a consistencyof the motion vector predictor candidates.
 44. The method of claim 43,wherein the consistency is a function of a difference between the motionvector predictor candidates that are available at both the video decoderand the corresponding encoder.
 45. The method of claim 37, wherein thecharacteristic comprises a fidelity of the motion vector predictorcandidates.
 46. The method of claim 45, wherein the fidelity is afunction of corresponding reconstructed residue coefficients which areavailable at both the video decoder and the corresponding encoder. 47.The method of claim 37, wherein the characteristic comprises a referenceframe index of the motion vector predictor candidates.
 48. The method ofclaim 37, wherein the motion vector predictor candidates comprise afirst motion vector predictor candidate for a first component of amotion vector and a second motion vector predictor candidate for asecond component of the motion vector, and an order of the second motionvector predictor candidate for the second component is adaptedresponsive to a predictor index of the first component.
 49. A computerreadable storage media having video signal data encoded thereupon,comprising: a block in a picture encoded by selecting an order of motionvector predictor candidates for the block responsive to a characteristicavailable at both the video encoder and a corresponding decoder, whereinthe characteristic excludes a mode in which the block is partitioned.